The present invention is directed to obstacle awareness systems, in general, and more particularly to a wide field scanning obstacle awareness system.
A common flight hazard of any aircraft operating near the Earth is the potential for collision with ground structures and obstacles. Helicopters, in particular, and now new classes of aircraft known as unmanned air vehicles (UAVs), often operate less than five hundred feet above ground level (AGL). In this environment, it is not uncommon for these aircraft to collide with electrical power lines, support wires for radio towers, or various structures and obstacles. These collisions typically result in loss of life, significant aircraft damage, damage to the structures or obstacles themselves, subsequent loss of power distribution on the electrical grid, and danger to persons and property on the ground. Aircraft, such as helicopters and UAVs, for example, typically operate in these low altitudes for take-off and landing, various low-level military maneuvers, and commercial applications, such as electrical utility inspection or emergency rescue missions.
Inspecting electrical power lines from an aircraft requires flying close to the Earth along high tension power lines and support structures looking for damaged equipment. Use of helicopters permit electric utility inspection crews to cover a large area of the power grids over a short period of time. Other helicopter applications which require low flying flight profiles include emergency and rescue missions, medical emergencies, border surveillance, and supply of floating oil platforms, for example. Likewise, UAV applications require autonomous control for surveillance, take-off, landing and delivery of munitions. In all of these applications, the flight crew and aircraft are at risk of colliding with obstacles like power lines, cables, towers, and other similar support structures. The risk becomes even greater with poor visibility and flights over unknown terrain. Depending on the type of aircraft canopy, the lighting, and the environmental conditions, many obstacles may become effectively invisible to the pilot and crew due to background clutter even under daylight conditions. Also, because of the narrow field of view offered the pilot by the aircraft, some obstacles may not be seen until it is too late for avoidance. Surprisingly, the highest accident rates are typically associated with clear conditions which indicates that during reduced states of pilot situational awareness, identification of hazardous ground obstacles may occur less regularly.
Some helicopters are equipped with structural wire strike protection kits which are fitted on the front end of the aircraft and intended to force a wire in the path of the aircraft to slide over the top or under the bottom of the aircraft. However, for this device to be effective, a contacted wire must slide across the canopy and into the wire cutters. When this occurs, the wire is likely to be severed by the wire cutter(provided it meets certain size and strength envelopes), freeing the aircraft from the hazards. It is not uncommon for electrical utility companies to identify cut wires but have no report of a wire strike accident. In some cases this indicates the flight crew did not know they hit a wire, much less cut it, or are reluctant to report the incident. However, if the wire does not slide across the canopy, and impacts other areas of the helicopter such as the rotors or landing skids, the wire cannot be severed by the wire strike protection system. As tension builds in the wire due to the forward motion, damage to the aircraft ensues with penetration into the canopy and flight crew, damage to the main rotor resulting in an imbalance, or loss of tail rotor control. In all these cases, the flight crew is in immediate life threatening danger. Depending upon the degree of interaction, fatalities can be attributed to the high-g accelerations of the rotor imbalance, blunt force trauma due to subsequent impact with the ground/aircraft, or harmful interactions with the wire resulting in significant lacerations or electrocution. Accordingly, due to the many low-level flying applications and the increasing risks posed thereby, obstacle avoidance warning systems for these aircraft have become of paramount importance for the safety of the pilot and crew of the aircraft. These devices are intended to warn the flight crew in advance of the collision with the obstacle, so that they(or an automated flight control system)can take evasive action prior to collision.
Amphitech International of Montreal, Canada, has developed a radar based obstacle awareness system named OASYS which was presented at the Quebec HeliExpo 2001. While it is proposed that OASYS can detect small obstacles, such as power lines, for example, up to two kilometers away even in adverse weather conditions, it is a rather heavy, bulky and costly unit, which may render it prohibitive for small aircraft usage.
Another obstacle awareness warning system is being developed by Dornier GmbH, in its Defense and Civil Systems Business Unit of Friedrichshafen, Germany under the tradename of HELLAS (Helicopter Laser Radar). In this unit, a laser beam is sequentially scanned through a line series of approximately one hundred optic fibers to create a raster line scan which is projected from the system. The line scan is steered vertically by a pivoted, oscillating mirror. The field-of-view is approximately plus and minus 32 degrees in azimuth and elevation with respect to a line of sight of the system. While Dornier promotes HELLAS as being an effective obstacle detection unit, it remains a relatively narrow field of view device that is rather complex and costly. In addition, the large number of optic fibers required for effective obstacle detection resolution, appears to render the device difficult to repeatedly align which may lead to manufacturing difficulties.
Another problem encountered in these low-level flight profile aircraft applications is the wind or air flow conditions surrounding the aircraft while it is carrying out its tasks. In some cases, an aircraft may encounter substantially different air-flow conditions from side to side. For example, when flying in a canyon, the aircraft may have a mountain wall on one side and open spaces on the other. Landing on the flight deck of an aircraft carrier poses similar risks. Such uneven air flow conditions may have an adverse affect on the responsiveness of the aircraft to the avoidance of detected obstacles.
Accordingly, it is desireable to have a wide field scanning laser based obstacle awareness system which is simpler in design and less costly than its predecessors to render it an economically attractive safety system for low-level flight profile aircraft. Combining air flow and obstacle measurements in a common system would provide the knowledge of air conditions surrounding the aircraft when an obstacle is detected in its flight path allowing a pilot to make his avoidance decisions based on such air data information. An enhanced situational awareness display would augment the peripheral vision of the flight crew to potential collision obstacles. The present invention is intended to provide for these desirable features in a laser based obstacle awareness system as will become more evident from the description thereof found herein below.
In accordance with one aspect of the present invention, A wide field scanning laser obstacle awareness system (LOAS) comprises: a plurality of first optical elements configured to direct a portion of a pulsed laser beam generated by a light source to a light detector, and to direct the pulsed laser beam to a beam expander wherein the pulsed laser beam is expanded; and at least one rotationally operated second optical element for directing the expanded pulsed laser beam from the system with a predetermined pattern scanned azimuthally over a wide field, the at least one rotationally operated second optical element also for receiving reflections of the pulsed laser beam from at least one object along the predetermined pattern and directing them to the laser beam expander wherein the laser beam reflections are focused; the plurality of first optical elements also configured to direct the focused laser beam reflections to the light detector for use in determining the location of the at least one object.
In accordance with another aspect of the present invention, the wide field scanning laser obstacle awareness system (LOAS) is used on-board an aircraft for alerting an operator of obstacles posing a risk of collision with the aircraft. For this purpose, the system additionally comprises: means for determining substantially the azimuth position of the directed pulsed laser beam; means for determining substantially the elevation of the directed pulsed laser beam; display apparatus; and wherein the processor means is coupled to the light detector, display apparatus, azimuth position determining means and elevation determining means for determining the location of the at least one object in range, azimuth and elevation in relation to a flight path of the aircraft, the processor means for driving the display apparatus to display an indication representing the at least one object in range, azimuth and elevation.
In accordance with yet another aspect of the present invention, Optical scanning apparatus controllable to project a plurality of different output scan patterns of a laser beam comprises: a first rotationally operated optical element for directing a laser beam, incident to a surface thereof, therefrom with an intermediate scan pattern; and a second rotationally operated optical element for directing the laser beam with the intermediate scan pattern from the apparatus with a desired output scan pattern, the first and second optical elements adjustably rotationally operated in relation to each other to effect the desired output scan pattern of the plurality of different output scan patterns of the laser beam.
In accordance with yet another aspect of the present invention, the scanning laser obstacle awareness system (LOAS) additionally comprises: a mirrored optical element disposed in the path of the pulsed laser beam between the plurality of first optical elements and the laser beam expander, the mirrored optical element rotationally operated about an axis thereof to effect a dithering of the pulsed laser beam before entering the laser beam expander wherein the dithered pulsed laser beam is expanded; the mirrored optical element and plurality of first optical elements also configured to direct the focused laser beam reflections to the light detector for use in determining the location of the at least one object.
In accordance with yet another aspect of the present invention, the wide filed scanning LOAS comprises: at least one scan head, each scan head including the laser beam expander; and at least one rotationally operated second optical element for directing the expanded pulsed laser beam from the scan head with the predetermined pattern, the at least one rotationally operated second optical element being rotated azimuthally by the scan head to scan the predetermined pattern over a wide azimuth field, the at least one rotationally operated second optical element also for receiving reflections of the pulsed laser beam from at least one object along the predetermined pattern and directing the laser beam reflections to the laser beam expander wherein the laser beam reflections are collected and returned to the plurality of first optical elements.